Polybenzimidazole is a non-flammable polymer which may be formed into textile fibers characterized by outstanding thermal, physical, and chemical stability. Processing parameters are well established for the extrusion of polybenzimidazole solutions into fibrous materials. Polybenzimidazole fibrous materials heretofore produced for textile applications commonly have exhibited a denier per filament of approximately 1.5.
Commonly assigned U.S. Pat. No. 3,441,640 broadly discloses a wet spinning method for the production of polybenzimidazole filaments having a denier per filament of 0.1 to 50. However, extremely fine filaments are not easily produced on a reliable basis by wet spinning methods. The unavoidable currents formed in the liquid as the polymer is extruded into it can disrupt the filaments. Also, the filaments tend to sag due to the fact that the horizontally extruded material has a higher specific gravity than the liquid of the spin bath.
Dry spinning processes, in which the polymer solution is extruded vertically downward into a hot stream of dry gas, have also been disclosed for the production of polybenzimidazole filaments. However, with super-fine filaments, the vertical distances commonly employed in such processes (e.g., 5 to 8 meters) may be a controlling factor since the filaments may not have sufficient strength to maintain integrity all the way to the bottom.
A dry jet/wet spinning process was disclosed in commonly assigned U.S. Pat. No. 3,851,025. That patent relates to the production of hollow polybenzimidazole filaments which are useful for specialized reverse osmosis applications. The patented process does not produce the ultralow denier filaments which are the subject of the present invention.
It is an object of the present invention to provide an improved process for the stable production of high-strength ultralow denier polybenzimidazole filaments.
It is an object of the present invention to provide a commercially practicable on-line, continuous process for the production of ultralow denier polybenzimidazole filaments without diminution of the desired tensile properties.
These and other objects, as well as the scope, nature, and utilization of the process will be apparent from the following description and appended claims.